Among various display devices such as a CRT, a LCD, a PDP (plasma display panel), and an EL (electroluminescence) display, a self-luminous display device such as the PDP and the EL display is superior in quality of displayed images.
However, the self-luminous display device consumes much electric power and it is necessary to lower its power consumption in order to reduce its negative influence to the environment and its running cost. In particular, necessity for reducing the power consumption increases as the size of the display device becomes larger.
Here, the necessity for reducing the power consumption is described in view of an emission mechanism of the self-luminous display device, with reference to an inorganic EL display device shown in FIG. 7 as an example of the self-luminous display device.
As shown in FIG. 7, the inorganic EL display device normally has a double insulating structure in which an emission layer 40 operated as an emission unit is inserted between insulating layers 30 and 50 and between electrodes 20 and 60a. The electrode 20 is on a substrate 10.
The insulating layers 30, 50 and the emission layer 40 are electrically capacitive loads. When alternating voltage is applied between the electrodes 20 and 60a, electric charge is stored by an amount depending on capacitances of the emission layer 40 and the insulating layers 30 and 50.
When the applied voltage exceeds a clamping voltage which depends on composition and film thickness of the emission layer 40 and the insulating layers 30 and 50, the stored charge flows in the emission layer 40 and collides with an emission core of the emission layer 40 to excite the emission core. The excited emission core emits light when its energy level drops to a ground state.
Since the inorganic EL display device is a capacitive load, electric current is generated with intensity depending on the capacitances of the emission layer 40 and the insulating layers 30 and 50, in storing and discharging the electric charge. In addition, the electric current is generated when the emission layer 40 emits the light in the emission mechanism described above. Therefore, the power consumption of the inorganic EL display increases as a display area becomes larger, because the capacitances of the elements 30, 40 and 50 increase as the display area becomes larger.
Therefore, in order to make the inorganic EL display achieve a large display area, a low operating voltage and a high brightness, it is necessary to reduce the power consumption. The necessity of reducing the power consumption is not specific to the inorganic EL display and is common to the self-luminous display device.